Biological Safety Cabinets

Biological Safety Cabinets (BSCs) are the primary means of containment for working safely with biohazardous material. BSCs are available that either exhaust to the outside or recirculate HEPA filtered air to the laboratory.

Types of Biological Safety Cabinets

Two classes of BSCs are described in this section, Class I and Class II. When combined with appropriate microbiological techniques, each class provides different levels of protection. Volatile and hazardous chemicals are not permitted in BSCs unless they are specifically designed for that purpose and are properly vented, and then only small amounts are allowed, with safe amounts determined by risk assessment. (see BMBL, page 388). All BSCs use HEPA filters to treat exhaust air. Class II cabinets filter both exhaust and intake air to protect the worker and the environment from contamination as well as to protect product in the cabinet. 

Class I Biological Safety Cabinets

Class I cabinets provide worker and environmental protection, but no product protection. Air drawn across the interior work surface is not HEPA filtered. There is a HEPA filter in the exhaust system to protect the environment. Class I cabinets may be used to enclose equipment or procedures with a potential to generate aerosols such as tissue homogenization, sonication, or cage dumping.

Class II Biological Safety Cabinets

Class II biological safety cabinets provide worker, environmental, and product protection. Both room air and interior cabinet air are drawn into a front grille creating an air barrier that provides personnel protection. In addition, downward laminar flow of HEPA-filtered air provides product protection. Air exhaust passes through a certified exhaust HEPA filter; it is particulate-free (environmental protection), and may be recirculated back into the laboratory (Type A1 and A2 BSCs without canopy unit) or discharged from the building via a canopy or “thimble” connected to the building. Exhaust air from Types B1 and B2 BSCs must be discharged directly to the outdoors via a hard connection.

The table below describes the various types of biological safety cabinets and the acceptable uses of each.

Types of Biosafety Cabinets

Types of Biosafety Cabinets
Type Worker Protection Product Protection Environmental Protection Volatile Chemicals and Radionuclides Nonvolatile Toxic Chemicals and Radionuclides Application
I Yes No Yes When exhausted to the outdoors1,2 Yes Enclose equipment or procedures with a potential to generate aerosols (tissue homogenization, cage cleaning, etc.).
II,A1 Yes Yes Yes No Yes (minute amounts) Cell culture and infectious material procedures that do not include the use of volatile chemicals.
II, A2 (was B3) Yes Yes Yes When exhausted to the outdoors1, 2 Yes Same as Type A1 but exhausted to outside. Minute quantities of volatile chemicals may be used.
II, B1 Yes Yes Yes Yes (minute amounts) 1,2 Yes Must be hard-ducted to exterior exhaust. Same procedures as Type II A1 but manipulations of minute quantities of volatile chemicals used with in vitro biological systems can be done.
II, B2 Yes Yes Yes Yes (minute amounts) 1,2 Yes Cabinet has total-exhaust, no air is recirculated. This cabinet provides simultaneous primary biological & chemical containment. Care must be given as some chemicals can damage the filters or gaskets.

1 Installation requires a special duct to the outside, an in-line charcoal filter, and a spark proof (explosion proof) motor and other electrical components in the cabinet. Discharge of a Class I or Class II, Type A2 cabinet into a room should not occur if volatile chemicals are used.
 2 In no instance should the chemical concentration approach the lower explosion limits of the compounds.

Source: Biosafety in Microbiological and Biomedical Laboratories